Frequency control apparatus, motor driving apparatus, and optical apparatus

ABSTRACT

A frequency control apparatus includes a signal generator configured to generate an output signal as a digital signal having a target frequency that has been set, using a plurality of signals having frequencies that are different from the target frequency and one another, an estimator configured to estimate a mixed frequency that is a frequency of a signal component mixed in the output signal and different from the target frequency and each of frequencies of the plurality of signals, and a frequency shift unit configured to shift at least one of the target frequency and the frequencies of the plurality of signals in accordance with an estimation result of the mixed frequency.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a frequency control apparatus using aPDM system and a motor driving apparatus configured to drive a vibrationmotor using the same.

Description of the Related Art

One of the pulse modulation systems is a Pulse Frequency Modulation(PFM) system configured to modulate a frequency of a carrier period. ThePFM system is classified into a system configured to steplessly change afrequency, and a system configured to simulatively change a frequency bythinning out a frequency clock to be used. The illustrative formersystem is a Voltage Controlled Oscillator (VCO) system that can obtain acomparatively fine frequency resolution for an input voltage. Theillustrative latter system is a Pulse Density Modulation (PDM) systemthat increases the frequency resolution by changing an average frequencyper a unit time period while maintaining constant the input clock. ThePDM system that can be implemented by a digital circuit is economicallymore advantageous than the VCO system that can be implemented by ananalogue circuit.

Since the PDM system obtains a high frequency resolution by changing thefrequency for each predetermined time period and by averaging the resultalong the time axis, the output frequency does not become constant andscatters when it is observed at predetermined time intervals. Therefore,in controlling the driving system to which an output signal generated bythe PDM method (PDM control) is input, the frequency scattering in thePDM control causes an uneven speed profile for the driving system and asignal in an audible band.

Japanese Patent No. 4838567 discloses a motor driving apparatus thatmakes high a resolution of the driving frequency applied to thevibration motor by the PDM control using an adder, and controls a motorby adding random noises to the frequency scattering by the PDM controlusing the adder. The motor control apparatus adds the random noises,disperses the frequency, and reduces a frequency component having a highspectrum for a specific setting oscillatory frequency and thereby apeaky frequency spectrum in the audible band.

However, the motor driving apparatus disclosed in Japanese Patent No.4838567 simply disperses the spectrum intensity by adding the randomnoises to the periodical frequency component different from the drivingfrequency. This motor driving apparatus can disperse the frequencyspectrum intensity and prevent the frequency component having a highspectrum intensity in the audible band, but the signal in the audibleband itself remains. Hence, the signal in the audible band (noise) maybe amplified by the resonance in the motor installed apparatus, etc. Inaddition, the frequency scattering may increase at predetermined timeintervals due to the random noises, and the uneven speed of the drivingsystem may increase.

SUMMARY OF THE INVENTION

The present invention provides a frequency control apparatus and a motordriving apparatus having the same, etc. which can control a frequency bya PDM system so as to prevent an unnecessary frequency component frombeing contained in a specific band.

A frequency control apparatus according to the present inventionincludes a signal generator configured to generate an output signal as adigital signal having a target frequency that has been set, using aplurality of signals having frequencies that are different from thetarget frequency and one another, an estimator configured to estimate amixed frequency that is a frequency of a signal component mixed in theoutput signal and different from the target frequency and each offrequencies of the plurality of signals; and a frequency shift unitconfigured to shift at least one of the target frequency and thefrequencies of the plurality of signals in accordance with an estimationresult of the mixed frequency.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a vibrationmotor driving apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a block diagram illustrating a configuration of an oscillatorfor a PDM control with an adder system according to the firstembodiment.

FIG. 3 is a view for explaining a change of a counted value by a counterin a PDM control according to the first embodiment.

FIG. 4 is a view illustrating a relationship between a behavior of thecounter and a pulse output in the PDM control in a vibration motordriving circuit according to the first embodiment.

FIG. 5 is a flowchart of a process driven with a constant frequency bythe vibration motor driving apparatus according to the first embodiment.

FIG. 6 is a view illustrating a relationship between an actual modulatedfrequency that occurs for the setting oscillatory frequency, and anestimated modulated frequency.

FIG. 7 is a block diagram illustrating a configuration of an AF systemin an image capturing apparatus according to a second embodimentaccording to the present invention.

FIGS. 8A and 8B are flowcharts of focus lens driving processes accordingto the second embodiment.

FIG. 9 is a view illustrating a relationship among a setting oscillatoryfrequency, a first estimated modulated frequency, and a second estimatedmodulated frequency according to the second embodiment.

DESCRIPTION OF THE EMBODIMENTS

A description will now be given of embodiments of the present inventionwith reference to the accompanying drawings.

First Embodiment

FIG. 1 illustrates a configuration of a vibration motor drivingapparatus that includes a frequency control apparatus according to afirst embodiment of the present invention. In FIG. 1, the vibrationmotor includes an oscillating object 170, a piezoelectric element 180 asan electrical-mechanical energy conversion element, and a mover 160 as acontact member. The vibration motor driving apparatus includes amicrocomputer (referred to as a “CPU” hereinafter) 120, an A-modeamplifier 130, a B-mode amplifier 140, an oscillator 100, an estimator(frequency shift unit) 110, and a position detector 150. The CPU 120,the oscillator 100, and the estimator 110 constitute a frequency controlapparatus. The CPU 120 and the oscillator 100 constitute a signalgenerator, and the estimator 110 constitutes an estimator and thefrequency shift unit. The CPU 120, the oscillator 100, and the estimator110 are comprised by a single computer or separate computers.

In the vibration motor, the piezoelectric element 180 to which atwo-phase frequency signal (driving signal) having mutually phasedifferences is applied produces a harmonic vibration. The oscillatingobject 170 is an elastic member coupled with the piezoelectric element180, and the vibration of the piezoelectric element 180 excites twooscillation modes (A mode and B mode) of bending vibrations. The A modeis a secondary bending vibration mode in a long side direction of theoscillating object 170, and the B mode is a primary bending vibrationmode in a short side direction of the oscillating object 170. A temporalphase difference between the A and B modes of vibrations can create anelliptical motion on a surface of the oscillating object 170. The mover160 compressively contacts the oscillating object 170, and movesrelative to the oscillating object 170 due to the friction with theoscillating object 170. Thus, the oscillating object 170 and the mover160 move relative to each other.

The CPU 120 governs controls over the entire vibration motor drivingapparatus. The CPU 120 outputs a signal indicative of a settingoscillatory frequency (target frequency) FREQ as an oscillatoryfrequency set (designated) from the outside as a frequency of the outputpulse. This setting oscillatory frequency FREQ is output to theoscillator 100 as the setting oscillatory frequency FREQ′ via afrequency shift process, which will be described later, at the estimator110. The CPU 120 outputs, to the oscillator 100, a signal indicative ofa set phase difference PHASE set from the outside as a phase differencebetween the A and B modes. The CPU 120 outputs, to the oscillator 100, asignal indicative of a pulse duty ratio DUTY set from the outside as apulse duty ratio, and a signal indicative of an output enablement ENABLEof the oscillator 100. The oscillator 100 performs an oscillationoperation for generating an output signal used to drive the vibrationmotor in the A and B modes in accordance with FREQ′, PHASE, DUTY, andENABLE.

The oscillator 100 includes a counter of a predetermined bit number (30bits in this embodiment, and CNT_(max)=2³⁰−1 where CNT_(max) is themaximum count value), and a comparator configured to determine whetherthe current count value is equal to or higher than a threshold countvalue.

The A-mode amplifier 130 amplifies an A-mode driving signal, and appliesit to the vibration motor via an inductor. The B-mode amplifier 140amplifies a B-mode driving signal, and similarly applies it to thevibration motor via an inductor.

The position detector 150 detects a moving amount or position of themover 160, and outputs the detection result to the CPU 120. The CPU 120controls driving of the vibration using position information obtainedfrom the position detector 150 and speed information calculated from theposition information.

The present invention is not limited to this embodiment that supplies atwo-phase driving signal to the oscillating object 170 that oscillatesin the two driving modes.

Next follows a description of a principle of a signal generation(referred to as a “PDM control of an adder system” or simply “PDMcontrol” hereinafter), with reference to FIG. 2. The driving signalcontains a signal component of a modulated frequency as a mixedfrequency different from a driving frequency that is a frequency of thedriving signal or a “modulated frequency is generated.” A cause will bedescribed below. This embodiment performs a frequency shift processconfigured to change or shift a setting oscillatory frequency so as toavoid the modulated frequency from occurring in the prohibited frequencyband as the specific frequency band by the PDM control with the settingoscillatory frequency FREQ. The frequency shift process will bedescribed later in detail, and the setting oscillatory frequency thathas received the frequency shift process will be referred to as apost-shift setting oscillatory frequency hereinafter.

FIG. 2 illustrates a configuration of the oscillator 100. The oscillator100 includes an adder 101, an A-mode comparator 102, a B-mode comparator103, an A-mode amplifier 104, and a B-mode amplifier 105.

The adder 101 includes a counter, and adds the following added value ata clock period with the post-shift setting oscillatory frequency FREQ′.

The A-mode comparator 102 compares the count value from the adder 101with the compared value set by DUTY, and generates an output signal(referred to as a “A-mode output pulse” hereinafter) as a pulsed digitalsignal in accordance with the comparison result. The A-mode comparator102 can set a pulse width or a leading edge timing of the output signalin accordance with the set value of DUTY set from the outside.

The B-mode comparator 103 compares the count value from the adder 101with the compared value set by DUTY and PHASE, and generates an outputsignal (referred to as a “B-mode output pulse” hereinafter) as a pulseddigital signal in accordance with the comparison result. Similar to theA-mode comparator 102, the B-mode comparator 103 can set the pulse width(leading edge timing of the output signal) in accordance with the setvalue of DUTY set from the outside. PHASE sets a count value with whichthe B-mode output pulse becomes high or low relative to the A-modeoutput pulse for the B-mode comparator 103.

The A-mode amplifier 104 amplifies and outputs the A-mode output pulsefrom the A-mode comparator 102, and the B-mode amplifier 105 amplifiesand outputs the B-mode output pulse from the B-mode comparator 103.

Next follows a description of a cause of the frequency scattering in apredetermined period of a pulse output in the PDM control of the addersystem.

FIG. 3 is a graph in which each block dot presents a locus of a countvalue when the counter adds a certain added value for each set clockperiod. In FIG. 3, the ordinate axis denotes a count value of the adder101, and the abscissa axis denotes time. The added value CNT_(add) canbe calculated as follows using the post-shift setting oscillatoryfrequency FREQ′[Hz] input to the adder 101, a clock frequency CLK [Hz],and a count upper limit value CNT_(max):

CNT_(add)=FREQ′×(CNT_(max)+1)/CLK.

When the added values CNT_(add) is repetitively added for each clockperiod from the count lower limit value, the counter will be sometimeoverflown or the count value exceeds the count upper limit value. Atthis time, the count value returns to 0, and the added value CNT_(add)is added to the surplus value at the overflow for each clock period.When CNT_(add) is constant, the count value draws a triangular wave(sawtooth) locus having a constant slope with a temporal change, asillustrated in FIG. 3.

Where a count period is defined as a time period for the count value tochange from the count lower limit value to the count upper limit value(actually a value close to the count upper limit value), an initialvalue (surplus value at the overflow) is different for each count periodwhen the overflow occurs. When the initial value is smaller than acertain value (a change amount of a surplus value in the count periodinterval), the number of additions of CNT_(add) in the same count periodincreases by one.

When the number of additions increases by one, the output pulse periodbecomes longer by 1/CLK [sec]. This is a cause of the frequencyscattering in the PDM control of the adder system. Hence, a frequencyhigher than the post-shift setting oscillatory frequency FREQ′ does notoccur. In addition, the modulated frequency depends on the magnitude ofthe surplus value in the overflow of the counter (strictly speaking achange amount of the surplus value in the count period interval). Thus,as the surplus value is larger, the high frequency component is morelikely to occur. A maximum value of the modulated frequency becomes thesetting oscillatory frequency/2. If the surplus value is 0 or if(CNT_(max)+1) is dividable by CNT_(add), the modulated frequency doesnot occur.

As illustrated in FIG. 3, in the first count period, CNT_(add) is addedtotally N+1 times, and the counter is overflown by the (N+2)-thaddition. In the second count period, the count accumulation starts withan initial value of an overflow surplus value Surplus1 in the firstperiod, CNT_(add) can be added by N times, and the counter is overflownat the (N+1)-th addition. CNT_(add) is added (N+1) times in the thirdperiod and N times in the fourth period due to the count period. Thenumber of additions is different according to the count period. The PDMcontrol is characterized in that the number of additions is differentdue to the period. The modulated frequency may overlap an audible bandfor the user and/or the resonance band for the driving system dependingon the frequency of the addition number change by the count period, andthe negative influence may occur on the control and quality.

For example, when the clock frequency CLK is 40 MHz, the count upperlimit CNT_(max) is 2³% and the post-shift setting oscillatory frequencyFREQ′ is 70 kHz, the added value CNT_(add) becomes 1879048.192. When theadder 101 does not deal with a floating point, a decimal is disregardedand CNT_(add) is expressed as 1879048. This value is added to thecounter for each clock period, and the value exceeds the count upperlimit value CNT_(max) at the 572^(nd) period.

The initial value is set to 1073631 in the next count period, andCNT_(add) is added for each clock period. In the second count period,the value exceeds the count upper limit CNT_(max) at the 571^(st) clockperiod. In the subsequent count period, the value exceeds the countupper limit value CNT_(max) at the 572^(nd) clock period, the 571^(nd)clock period, the 572^(nd) clock period, the 571^(nd) clock period, the572^(nd) clock period, the 571^(nd) clock period, the 572^(nd) clockperiod, the 571^(nd) clock period, . . . .

The frequency (first frequency) corresponding to the 572^(nd) clockperiod is 69.3006993 kHz, and the frequency (second frequency)corresponding to the 571^(nd) clock period is 70.0525394 kHz. Theoscillator 100 realizes 70 kHz as the post-shift setting oscillatoryfrequency FREQ′ by adjusting the appearance ratio of these twofrequencies. In this example, the modulated frequency occurs at about 35kHz and about 10 kHz. At which clock in which clock period the counteris overflown is found by a recursive and repetitive calculation or by afrequency analysis on the pulse output. However, due to a highcalculation cost, the calculation processing apparatus having a moderatecalculation capability, such as a microcomputer, has a heavy processingload. Accordingly, this embodiment realize the PDM control that reducesthe calculation cost by estimating the modulated frequency, and canprevent the modulated frequency in the predetermined band.

Referring to FIG. 4, a description will be given of how the oscillator100 having the configuration illustrated in FIG. 2 provides thetwo-phase output signal (A-mode output signal and B-mode output signal).Similar to FIG. 3, the top in FIG. 4 illustrates a graph made with alocus of black dots as added values in the counter for each set clockperiod where the ordinate axis represents a count value of the adder 101and the abscissa axis represents time. The bottom in FIG. 4 illustratesthe A-mode output pulse and the B-mode output pulse in order from thetop.

DUTY is represented by 0 to 100% in a high section of a pulsed output,and the value of the count value×(100−DUTY) is set to a compared value(predetermined value) in accordance with the set value, and the A-modecomparator 102 performs comparison matching. The compared value is avalue between the count lower limit value and the count upper limitvalue. At the timing when the count value is larger than the comparedvalue, the A-mode output pulse becomes high, the counter is overflown,and the high state continues till the next count period starts. Whilethe count value is smaller than the compared value in the next countperiod, the A-mode output pulse is low.

Since DUTY equivalent with that of the A mode is also set to the B mode,the high and low section have basically equal widths, although they arenot perfectly equal to each other due to the same cause of the frequencyscattering in the PDM control. Moreover, the set value of PHASE causesthe phase difference between the B-mode output pulse and the A-modeoutput pulse to be set. For example, assume that PHASE is 90 degrees.Then, the count period is 360 degrees. The compared value in the B-modecomparator 103 is made by adding CNT_(max)/4 to the compared value setin the A-mode comparator 102. The compared value at the leading edgetiming for the B-mode comparator 103 is also set.

FIG. 3 illustrates that the modulated frequency is caused by the surplusvalue that occurs based on the relationship between the count upperlimit value and the added value. When the count upper limit value isconverted into a compared value set to each of the A mode comparator 102and B mode comparator 103, a similar phenomenon occurs. This embodimentis applicable to a modulated frequency that occurs due to the duty ratioand phase difference settings.

The vibration motor as a driven object for the vibration motor drivingapparatus according to this embodiment is driven with an oscillatoryfrequency band higher than the human audible band. The modulatedfrequency occurs in the PDM control as described above only in afrequency band lower than the setting oscillatory frequency.

Based on the above precondition, this embodiment sets the prohibitedfrequency band (specific frequency band) to 20 Hz to 20 kHz as the humanaudible band, and estimates one of the plurality of modulatedfrequencies that occur in the PDM control. This embodiment estimates themodulated frequency (low frequency) lower than at least one of theplurality of modulated frequency.

Herein, the following relationship is established where Q₁ is a quotientof (CNT_(max)+1)/CNT_(add), S₁ is a surplus (remainder) of(CNT_(max)+1)/CNT_(add), CNT_(max) is the count upper limit value, andthe added value CNT_(add) is made by converting the post-shift settingoscillatory frequency added to each other for each clock:

(CNT_(max)+1+S ₁)/CNT_(add) =Q ₂ * * * S ₂

The clock frequency up to the overflow in the second count period andthe initial value in the third count period can be expressed with thequotient Q₂ and the surplus S₂ in the above expression.

The following estimated modulated frequency FREQ_(est.1) is a value madeby converting into a frequency an absolute value of a difference betweenthe surplus S₁ in the first count period and the surplus S₂ in thesecond count period:

FREQ_(est.1) −|S ₁ −S ₂|×CLK/(CNT_(max)+1)

This embodiment determines whether the modulated frequency FREQ_(est.1)is included in the prohibited frequency band, based on the estimationresult.

Referring now to the flowchart in FIG. 5, a description will be given ofprocesses performed by the CPU 120 and the estimator 110 when thevibration motor according to this embodiment is driven at a constantfrequency. The CPU 120 and the estimator 110 execute these process inaccordance with a driving control program as a computer program. Thedriving control program includes a frequency control program thatperforms a frequency shift process for the setting oscillatoryfrequency.

In the step S101, the CPU 120 obtains a state of the vibration motordriving apparatus (referred to as a “motor driving apparatus”hereinafter). The vibration motor is subject to the temperaturecharacteristic of the piezoelectric element and a deterioration causedby the abrasion between the oscillating object and the contact member,and the oscillatory frequency characteristic (such as a startoscillatory frequency when driving starts) in the driving may be changedas the driving environment changes. Hence, the CPU 120 that has receivedthe driving process command obtains temperature information from anunillustrated temperature sensor and the sequentially stored drivingnumber of the vibration motor from an unillustrated memory.

Next, in the step S102, the CPU 120 obtains the setting oscillatoryfrequency FREQ, the set duty ratio DUTY, and the set phase differencePHASE between A and B modes, from the unillustrated memory, and outputs(sets) only the setting oscillatory frequency FREQ to the estimator 110.The CPU 120 outputs, as the setting oscillatory frequency FREQ, a fineadjusted value of the setting oscillatory frequency stored in the memoryin accordance with the temperature information and the driving numberinformation obtained in the step S101.

In the step S103, the CPU 120 calculates the added value CNT_(add) foreach clock period for the adder 101 corresponding to the settingoscillatory frequency FREQ set in the step S102. As described above, theadded value CNT_(add) can be calculated by the following expressionwhere the counted upper limit value is CNT_(max) and the clock frequencyis CLK:

CNT_(add)=FREQ×(CNT_(max)+1)/CLK

The estimator 110 rather than the CPU 120 may perform this process.

Next, in the step S104, the estimator 110 estimates the modulatedfrequency that would occur when the setting oscillatory frequency FREQis output to the oscillator 100. As described above, the estimatedmodulated frequency FREQ_(est.1) is estimated by converting the absolutevalue of the difference into the frequency between the surplus value S₁that occurs in the overflow in the first count period and the surplusvalue S₂ that occurs in the overflow in the second count period or bythe calculation of |S₁−S₂|×CLK/(CNT_(max)+1).

Next, in the step S105, the estimator 110 determines whether theestimated modulated frequency FREQ_(est.1) calculated in the step S104is located in the prohibited frequency band. The prohibited frequencyband is set to 20 Hz to 20 kHz as the human audible band, as describedabove. When the estimated modulated frequency FREQ_(est.1) is located inthe prohibited frequency band, the PDM control with the settingoscillatory frequency FREQ set in the step S102 causes the modulatedfrequency to fall within the prohibited frequency band and it is thusnecessary to shift (change) the oscillatory frequency. Hence, theestimator 110 moves to the step S106. On the other hand, when theFREQ_(est.1) is not located in the prohibited frequency band, the flowmoves to the step S108.

In the step S106, the estimator 110 calculates a frequency shift amountΔFREQ from the setting oscillatory frequency FREQ so that the estimatedmodulated frequency is located outside of the prohibited frequency band,and performs a frequency shift process for calculating the post-shiftsetting oscillatory frequency FREQ′. The post-shift setting oscillatoryfrequency FREQ′ is expressed by FREQ±ΔFREQ. The frequency shift amountΔFREQ is calculated using the following expression with the estimatedmodulated frequency FREQ_(est.1) and the highest frequency(FREQ_(SPC)=20 kHz) in the prohibited frequency band:

ΔFREQ=(20 kHz−FREQ_(est.1))/Q ₁

In this expression, Q₁ is the number of additions just before theoverflow in the first count period. A sign of ΔFREQ becomes plus whenS₁−S₂ becomes a negative value, meaning a shift to the high frequencyside. The sign of ΔFREQ becomes minus when S₁−S₂ becomes a positivevalue, meaning a shift to the low frequency side.

The above process can set the post-shift setting oscillatory frequencyFREQ′ so as to prevent the modulated frequency from being located in theprohibited frequency band, and to minimize the shift amount from thesetting oscillatory frequency FREQ set in the step S102.

The prohibited frequency band on the high frequency side has beenhitherto described. When the estimated modulated frequency FREQ_(est.1)is closer to 20 Hz as the low frequency side of the prohibited frequencyband, the post-shift setting oscillatory frequency FREQ′ may be set to afrequency that does not cause the modulated frequency as describedlater. The counter in the adder 101 in this embodiment can count up to2^(n), and the count upper limit value CNT_(max) also has a function ofn or 2^(n)−1. In other words, the post-shift setting oscillatoryfrequency FREQ′ may have a value such that the added value CNT_(add) canbe expressed by a power of two. Hence, the added value is set to a powerof two closest to the added value CNT_(add) corresponding to the settingoscillatory frequency FREQ calculated in the step S103, and the valueconverted into the frequency is the post-shift setting oscillatoryfrequency FREQ′.

This embodiment allows the modulated frequency of 0 in the modulatedfrequencies below 20 Hz so as to shorten the calculation time period.The modulated frequency of 0 means that the frequency of the signaloutput by the PDM control can be singularly realized.

Next, in the step S107, the estimator 110 calculates the added valueCNT_(add) for each clock period for the adder 101 corresponding to thepost-shift setting oscillatory frequency FREQ′ calculated in the stepS106. Similar to the step S103, the added value CNT_(add) can beexpressed as follows where CNT_(max) is the count upper limit value andCLK is the clock:

CNT_(add)=FREQ′×(CNT_(max)+1)/CLK

The CPU 120 rather than the estimator 110 may execute this process.Thereafter, the CPU 120 moves to the step S108.

In the step S108, the CPU 120 settles the post-shift setting oscillatoryfrequency FREQ′ calculated by the estimator 110 in the step S106 asinformation output to the oscillator 100. When it is determined that themodulated frequency that would occur for the setting oscillatoryfrequency FREQ in the step S105 is not located in the prohibitedfrequency band, a relationship of FREQ=FREQ′ is established.

Next, in the step S109, the CPU 120 outputs the output enablement ENABLEto the oscillator 100. Moreover, the CPU 120 outputs the set duty ratioDUTY set in the step S102, the set phase difference PHASE between the Aand B modes, and the post-shift setting oscillatory frequency FREQ′settled in the step S108 to the oscillator 100.

Due to the above process, the added value CNT_(add) is accumulated inthe counter in the adder 101 for each clock period, and the outputs ofthe two-phase A-mode and B-mode output pulses to the vibration motorchange when the count value reaches the predetermined value or higher.Since this embodiment maintains constant the duty ratio and the phasedifference between the A and B modes, the modulated frequency may beestimated only once when the driving of the vibration motor starts.

When the vibration motor is again driven, the state of the motor drivingapparatus may change and the setting oscillatory frequency differentfrom the previous one may need to be set in the step S102. It is thusnecessary to estimate the modulated frequency whenever the drivingstarts. Since the setting oscillatory frequency is different wheneverthe motor is driven, the modulated frequency by the PDM control is morefrequently calculated, but two surplus calculations are enough for theestimation method according to this embodiment. Even when theoscillatory frequency is to be changed, only one division may be addedand the increased calculation time period can be almost ignored.

Thus, a time lag from the driving setting to the actual driving start inthe vibration motor can be almost ignored, and the motor can be drivenat the driving frequency that can prevent the modulated frequency fromentering the prohibited frequency band. This embodiment sets theprohibited frequency band to the audible band, but may set it to thefrequency band that cannot be used to control the vibration motor.

FIG. 6 illustrates the actual modulated frequency in the PDM control andthe estimated modulated frequency. The abscissa axis denotes a settingoscillatory frequency FREQ input to the oscillator 100 and the ordinateaxis denotes the modulated frequency.  and x plots are the estimatedmodulation frequency (“estimated frequency” in FIG. 6) and the actualmodulated frequency (“modulated frequency” in FIG. 6), respectively.Both plots represent changes of the estimated modulation frequency andthe actual modulated frequency when the counter added value CNT_(add) orthe setting oscillatory frequency FREQ is changed.

FIG. 6 illustrates that the estimated modulated frequency isperiodically output as a triangular (sawtooth) wave (where the amplitudedepends on the setting oscillatory frequency FREQ). Hence, when theestimated modulated frequency is known to the current settingoscillatory frequency, the frequency shift amount used to shift theestimated modulated frequency to the outside of the prohibited frequencyband is uniquely determined. The estimated modulated frequency forms atriangular wave because it is calculated from the absolute value ofS₁−S₂. When the calculation of the absolute value is omitted, theestimated modulated frequency forms a sawtooth wave. Thus, a sign of thefrequency shift amount ΔFREQ can be calculated from the sign of S₁−S₂.

When the estimated modulated frequency is close to the harmonic sideabove about 30 kHz, the estimation error to the actual modulatedfrequency increases. Since this embodiment sets the prohibited frequencyband to the human audible band (up to 20 kHz), the estimated error canbe ignored. In the overall range of the setting oscillatory frequency, arelationship of the actual modulation frequency the estimated modulatedfrequency is established, and thus the estimation of the modulatedfrequency and the frequency shift process in this embodiment areeffective in preventing the modulated frequency from entering theprohibited frequency band.

While this embodiment sets the prohibited frequency band to the humanaudible band, the prohibited frequency band may be set to the band thatcontains a resonance frequency of the vibration motor.

While this embodiment shifts the setting oscillatory frequency, at leastone of the first frequency (69.3006993 kHz) and the second frequency(70.0525394 kHz) used to generate the setting oscillatory frequency maybe shifted. Thereby, the modulated frequency may be avoided in theprohibited frequency band.

This embodiment generates the setting oscillatory frequency using two (aplurality of) signals having the first and second frequencies as thefrequencies different from the setting oscillatory frequency (targetfrequency). When the added value is expressed by 2^(n), the settingoscillatory frequency can be generated using the signal having onefrequency. The setting oscillatory frequency may be generated usingthree or more frequencies different from the setting oscillatoryfrequency. When the three or more frequencies are used, a controller isprovided to adjust appearance ratios of the first frequency and thesecond frequency and to realize the setting oscillatory frequency. Thecontroller variably controls the calculated added value CNT_(add) addedfor each clock period.

Second Embodiment

FIG. 7 illustrates a configuration related to an AF function in a camerasystem that includes an interchangeable lens 200 as an optical unitincluding a motor driving apparatus with a frequency control circuitaccording to the embodiment of the present invention, and a camera body300 to which the interchangeable lens 200 is detachably attached.

The camera body 300 includes a camera CPU 301, a focus detection unit302, an image sensor 303, and a camera communication unit 304. Thecamera CPU 301 controls all operations of the camera body 300. Thecamera CPU 301 includes a memory, such as a RAM, a ROM, and an EEPROM.The camera CPU 301 determines an in-focus position of the focus lens(optical element) 202 for the object in accordance with a focusdetection result in the focus detection unit 302, and sends a focusdriving command to the interchangeable lens 200 via the cameracommunication unit 304.

The focus detection unit 302 detects a focus state of an image capturingoptical system for the object using a light flux from the imagecapturing optical system in the interchangeable lens 200. The focusdetection method may be a phase difference detection method, a contrastdetection method, or another focus detection method.

The image sensor 303 includes a photoelectric conversion element, suchas a CMOS sensor and a CCD sensor. The image capturing optical system inthe interchangeable lens 200 forms an image using the light flux fromthe object, as an object image on the image sensor 303. This embodimentprovides focusing by moving the focus lens 202 in the image capturingoptical system in the optical axis direction, but may move the imagesensor 303 in the optical axis direction using the motor drivingapparatus for focusing.

The camera communication unit 304 includes a plurality of communicationterminals for communications between the camera CPU 301 and the lens CPU201, which will be described later, so as to provide a requesttransmission from the camera CPU 301 to the lens CPU 201 and aninformation transmission from the lens CPU 201 to the camera CPU 301.The interchangeable lens 200 supplies a power from the unillustratedpower unit in the camera body 300 via the camera communication unit 304.

The interchangeable lens 200 includes a lens CPU 201, the imagecapturing optical system (although only the focus lens 202 isillustrated in FIG. 7), the focus controller 203, the focus drivingcircuit 204, and the lens communication unit 205. The focus lens 202 isdriven by the vibration motor as a driving source (actuator) describedin the first embodiment with reference to FIG. 1. The focus controller203 and the focus driving circuit 204 constitute the motor drivingapparatus configured to drive the vibration motor.

The lens CPU 201 controls an operation in the interchangeable lens 200in accordance with a request from the camera CPU 301 and a state of eachcomponent in the interchangeable lens 200. The lens CPU 201 includes amemory, such as a RAM, a ROM, and an EEPROM.

The piezoelectric element 180 and the vibrator 170 illustrated in FIG. 1are attached to the focus lens 202. When the two-phase driving signaldescribed in the first embodiment is supplied from the focus drivingcircuit 204 described later to the piezoelectric element 180, theoscillating object 170 elliptically moves. The oscillating object 170contacts the contact member 160 fixed in the interchangeable lens 200.Thus, the focus lens 202 is driven in the optical axis direction by thefriction between the oscillating object 170 and the contact member 160.

The focus controller 203 includes a software and a hardware circuitconfigured to control an operation relating to the focus lens 202, andincludes the CPU 120 and the estimator 110 in the motor drivingapparatus illustrated in FIG. 1. The focus controller 203 outputs, tothe focus driving circuit 204, a driving command (driving speed, drivingamount, and driving direction) of the vibration motor in accordance withthe focus driving command from the camera CPU 301 via the lens CPU 201.The focus controller 203 detects the operation of an unillustratedmanual focus ring provided onto the interchangeable lens 200 via thelens CPU 201, and outputs the driving command for the vibration motor tothe focus driving circuit 204.

The interchangeable lens 200 includes a position detector (referred toas a “focus position detector” hereinafter). This embodiment performs afeedback control over driving of the vibration motor based on adeviation between position information of the focus lens 202 obtainedfrom the focus position detector 150 and a target position set by thefocus controller 203. A non-feedback control may be performed for thevibration motor, such as a feed forward control, a closed loop complexcontrol, an open loop control, and a sequence control.

While this embodiment drives the focus lens 202 using the vibrationmotor, a magnification varying motor (zoom lens) and an aperture stopmay be driven by the vibration motor and the motor driving apparatusdescribed in the first embodiment may be used for the vibration motor.

The focus driving circuit 204 drives a vibration motor by converting thedriving command from the focus controller 203. The focus driving circuit204 includes the oscillator 100, the A-mode amplifier 130, and theB-mode amplifier 140 in the motor driving apparatus illustrated in FIGS.1 and 2.

This embodiment calculates the estimated modulated frequency (firstestimated modulated frequency) calculated in the first embodiment andthe estimated modulated frequency (second estimated modulated frequency)closer to the low frequency side. In the following description, theactual modulated frequency corresponding to the first estimatedmodulated frequency will be referred to as a first modulated frequencyand the actual modulated frequency corresponding to the second estimatedmodulated frequency will be referred to as a second modulated frequency.

Where CNT_(max) is the count upper limit value of the adder 101 in theoscillator 100, CNT_(add) is the counter added value determined for thesetting oscillatory frequency, Q₁ is a quotient, and S₁ is a surplus,the following expression is established:

(CNT_(max)+1)/CNT_(add) =Q ₁ * * * S ₁

The surplus S₁ corresponds to the initial value in the second countperiod (overflow surplus value in the first count period).

Moreover, the following expression provides the quotient Q₂ and thesurplus S₂:

(CNT_(max)+1+S ₁)/CNT_(add) =Q ₂ * * * S ₂

The surplus S₂ corresponds to the initial value in the third countperiod (overflow surplus value in the second count period).

The initial value that fluctuates for each count period is expressedusing the surpluses S₁ and S₂. When FREQ_(est.1) is defined as the firstestimated modulated frequency as the estimated modulated frequencycalculated in the first embodiment, the following expression isestablished:

FREQ_(est.1) =|S ₁ =S ₂|×CLK/(CNT_(max)+1)

The first estimated modulated frequency FREQ_(est.1) can be rewritten asfollows using the setting oscillatory frequency FREQ and the counteradded value CNT_(add):

FREQ_(est.1)=FREQ/(CNT_(add) /|S ₁ −S ₂|)

The calculation (CNT_(add)/|S₁−S₂|) in the denominator on the right sideprovides a count period converted value corresponding to the timing atwhich the initial value of the count period exceeds CNT_(add). It is thetiming of the count period at which the number of additions decreases byone, and the first estimated modulated frequency can be calculated whenit is divided by the setting oscillatory frequency FREQ.

Next, the second estimated modulated frequency is calculated. The secondestimated modulated frequency can be calculated using a decimal part ofa where CNT_(add)/|S₁−S₂|=α. Assume that α_(int) is a natural numberpart of α and α_(dec) is a decimal part of α (α=α_(int)+α_(dec)). At thetiming when the number of additions is decreased one by the firstestimated modulated frequency, the counter may be overflown and thesurplus value may occur. It means that a plurality of modulatedfrequencies exist. When the accumulated surplus values caused by thefirst modulated frequency exceeds the counter added value CNT_(add), thetiming of the count period at which the number of additions decreasesone occurs at a timing different from that of the first modulatedfrequency. This is the second estimated modulated frequency, and thedecimal part α_(dec) of α represents the degree of the magnitude of thesurplus value.

Since the surplus value accumulated in a period of the first modulatedfrequency can be calculated as CNT_(add)−(|S₁−S₂|×α_(dec)) the secondestimated modulated frequency FREQ_(est.2) can be calculated as follows:

FREQ_(est.2)=FREQ/(CNT_(add)/(CNT_(add)−(|S ₁ −S ₂|×α_(dec))))

The repetitive recursive calculations using the decimal part of(CNT_(add)/(CNT_(add)(|S₁−S₂|×α_(dec)))) in the above expression canprovide all included modulated frequencies.

Assume that the prohibited frequency band is set to the human audibleband (20 Hz to 20 kHz), the clock frequency CLK of the oscillator 100 isset to 80 MHz, the count upper limit value CNT_(max) is set to 2³⁰−1,and a setting range of the setting oscillatory frequency is 50 to 120kHz. The probability where the first modulated frequency is locatedoutside of the prohibited frequency band is 50.0%, the probability wherethe second modulated frequency is located outside of the prohibitedfrequency band is 11.3%, and the probability where both the first andsecond modulated frequencies are located outside of the prohibitedfrequency band is only about 10.9%. Hence, the recursive estimation ofthe modulated frequency causes a very large shift amount to the outsideof the prohibited frequency band, and the driving system of thevibration motor may collapse. When the calculation time associated withthe recursive process is considered, it is useless to estimate modulatedfrequencies more than the second estimated modulated frequency.

Hence, this embodiment provides the estimations up to the secondestimated modulated frequency, and sets the prohibited frequency band to2 to 12 kHz for the first estimated modulated frequency and 3 to 5 kHzfor the second estimated modulated frequency. Thereby, under the aboveassumption, the setting oscillatory frequency that enables both thefirst modulated frequency and the second modulated frequency to belocated outside of the prohibited frequency band increases by about 61%in the overall range of 50 to 120 kHz.

Allegedly, the human audible band ranges from 20 Hz to 20 kHz, but theminimum audible value ranges from 1 to 5 kHz, and a person is generallymost sensitive to nearly 4 kHz. Since the sensitivity remarkablydeteriorates in the harmonic side above 15 kHz, a limited range of 1 to15 kHz appears proper when the audible band is redefined according tothe sensitivity. Since the sensitivity tends to be high in a lowfrequency band with a peak of nearly 4 kHz, this embodiment sets theprohibited frequency band near the low frequency. In other words, thisembodiment sets the prohibited frequency band so that both the first andsecond estimated modulated frequencies are not equal to about 4 kHz andthe frequency band above 60% of the overall range can be used.

Since the entire audible band is not set to the prohibited frequencyband, the frequency in the audible band may occur depending on thesetting oscillatory frequency. However, this embodiment can prevent themodulated frequency from being audible to a human using the prohibitedfrequency band. The prohibited frequency band may be properly set by anapplication, a condition, and an observer (user), and values in thisembodiment are merely illustrative.

The vibration motor in this embodiment is a driving source (actuator)used to drive the focus lens 202, and driven according to the focusdriving command from the camera 300 and the operation of the user, asdescribed above. The driving command (driving speed, driving amount anddriving direction) is different according to the state of theinterchangeable lens 200 and the object, and the variable control isnecessary for the driving speed of the vibration motor.

This embodiment makes constant the oscillatory frequency in the focusdriving circuit 204 (oscillator 100) in low speed driving, changes thephase difference between the A mode and the B mode, and controls thedriving speed of the vibration motor. This phase difference control canincrease the driving speed as the phase difference increases. When thephase difference reaches a certain value, control is switched at thattiming so that the phase difference at the switching time is maintainedconstant, the oscillatory frequency is changed, and the driving speed iscontrolled. This frequency control can increase the driving speed as theoscillatory frequency becomes lower. As described above, this embodimentperforms the phase difference control in the low speed range and thefrequency control in the high speed range.

The modulated frequency is estimated and the setting oscillatoryfrequency is shifted only in the phase difference control (or when thedriving starts). In the frequency control, the influence on the controldue to the low resolution of the oscillatory frequency to be expressedand the setting oscillatory frequency for each control periodsequentially change and the intensity of the specific frequency spectrumtemporally disperses. Thus, the modulated frequency is not estimated orthe setting oscillatory frequency is not shifted with the estimationresult.

Although not illustrated in FIG. 7, a directional microphone is providedused for the camera 300 to capture a motion image. In the motion imagecapturing, the modulated frequency is estimated and the settingoscillatory frequency is shifted so as to prevent the directionalmicrophone from detecting the component of the modulated frequency ofthe oscillator 100. In the motion image capturing, it is general torestrict a driving speed for each type of driving system in theinterchangeable lens 200 so as to restrain an increase of a drivingnoise and a rapid change of an image plane. This embodiment drives thevibration motor as an actuator configured to drive the focus lens 202 ina phase difference control range in the motion image capturing.

The estimation of the modulated frequency by the estimator 110 isswitched by the control state of the vibration motor irrespective of theimage capturing state of the camera 300. The estimation of the modifiedfrequency may be set in accordance with the control state of thevibration motor and the image capturing state of the camera 300. Forexample, in the frequency control state of the vibration motor in themotion image capturing, the prohibited frequency band may be set to anarrow band in accordance with the sensitivity characteristic of thedirectional microphone so as to widen the usable frequency band and toenhance the control stability.

Under the above condition, a description will be given of a process forcontrolling driving of the vibration motor (or driving of the focus lens202), with reference to flowcharts in FIGS. 8A and 8B. The lens CPU 201and the focus controller 203 execute this process in accordance with thefocus control program as a computer program. The focus control programcontains a frequency control program that performs the frequency shiftprocess for the setting oscillatory frequency.

In the step S201, the lens CPU 201 obtains the focus driving command(referred to as a “camera side focus driving command” hereinafter) sentfrom the camera CPU 301. The camera CPU 301 obtains the focus state ofthe image capturing optical system through the focus detection unit 302,and calculates the driving amount and the driving direction of the focuslens 202 based on the focus state. The camera CPU 301 sends the cameraside focus driving command containing the driving amount and the drivingdirection of the focus lens 202, to the lens CPU 201.

The camera side focus driving command contains information indicative ofthe state of the camera 300, such as setting of the still image/motionimage capturing modes, and whether the motion image is being captured).This information is used for the lens CPU 201 to limit the driving speedof the vibration motor.

The focus controller 203 (CPU 120) sets the target position and thedesignated speed for the focus lens 202 based on the camera side focusdriving command received via the lens CPU 201. When the designated speedis below the predetermined value, the vibration motor is driven basedonly on the phase difference control, and when the designated speed isequal to or above the predetermined value, the vibration motor is drivenbased on a combination of the phase difference control and the frequencycontrol.

Separate from the camera side focus driving command, the lens CPU 201outputs, to the focus controller 203, a lens side focus driving commandin accordance with an operation of the user of the above manual focusring provided onto the interchangeable lens 200. The focus controller203 (CPU 120) sets the target position and the designated speed of thefocus lens 202 based on the lens side focus driving command similar tothe case where the focus controller 203 receives the lens side focusdriving command. The information indicative of the state of the camera300 may be obtained from the camera CPU 301 at that time, or thepreviously obtained information may be utilized.

Next, in the step S202, the focus controller 203 (CPU 120) obtains thestate of the vibration motor. The vibration motor is subject to thetemperature characteristic of the piezoelectric element and adeterioration caused by the abrasion between the oscillating object andthe contact member, and the oscillatory frequency characteristic (suchas a start oscillatory frequency at the driving start) in the drivingmay be changed when the driving environment changes. Hence, the CPU 201that has received the driving process command obtains the temperatureinformation from the unillustrated temperature sensor and thesequentially stored driving number of the vibration motor from theunillustrated memory.

Next, in the step S203, the focus controller 203 (CPU 120) obtains thesetting oscillatory frequency FREQ, the set duty ratio DUTY, and the setphase difference PHASE between A and B modes, from the unillustratedmemory, and outputs (sets) only the setting oscillatory frequency FREQto the estimator 110 in the focus controller 203. The focus controller203 outputs, as the setting oscillatory frequency FREQ, the fineadjusted setting oscillatory frequency stored in the memory inaccordance with the temperature information and the driving numberinformation obtained in the step S202.

In the step S204, the focus controller 203 calculates the added valueCNT_(add) for each clock period for the adder 101 in the focus drivingcircuit 204 corresponding to the setting oscillatory frequency FREQ setin the step S203. The added value CNT_(add) can be calculated by thefollowing expression where CNT_(max) is the count upper limit value andCLK is the clock frequency:

CNT_(add)=FREQ×(CNT_(max)+1)/CLK

Next, in the step S205, the focus controller 203 (estimator 110)estimates the first and second estimated modulated frequenciesFREQ_(est.1) and FREQ_(est.2) when the oscillator 100 in the focusdriving circuit 204 outputs the setting oscillatory frequency FREQ. Asdescribed above, the estimation modulated frequency FREQ_(est.1) isestimated by converting the absolute value of the difference into thefrequency between the surplus value S₁ that occurs in the overflow inthe first count period and the surplus value S₂ that occurs in theoverflow in the second count period or by the calculation of|S₁−S₂|×CLK/(CNT_(max)+1).

The second estimated modulated frequency FREQ_(est.2) can be calculatedfrom an overflow value of the counter that occurs with the firstmodulated frequency. More specifically, where α_(dec) is a decimal partof the calculation result of (CNT_(add)/|S₁−S₂|), the second estimatedmodulated frequency FREQ_(est.2) can be estimated usingFREQ/(CNT_(add)/(CNT_(add)−(|S₁−S₂|×α_(dec)))).

In the step S206, the focus controller 203 (estimator 110) determineswhether the first and second estimated modulated frequenciesFREQ_(est.1) and FREQ_(est.2) calculated in the step S205 are located inthe prohibited frequency band. As described above, the prohibitedfrequency band is set to 2 to 12 kHz for the first estimated modulatedfrequency and 3 to 5 kHz for the second estimated modulated frequency.The determination expression is a logic disjunction between the factthat both the first and second estimated modulated frequenciesFREQ_(est.1) and FREQ_(est.2) are located outside of the prohibitedfrequency band, and the fact that counter added value CNT_(add) isdivided by two (or that no modulated frequency occurs). When thedetermination expression is not satisfied, the modulated frequencyoccurs in the prohibited frequency band due to the PDM control with thesetting oscillatory frequency FREQ set in the step S202, and it isnecessary to shift the setting oscillatory frequency. Therefore, thefocus controller 203 (estimator 110) moves to the step S207. On theother hand, when the determination expression is satisfied, the flowmoves to the step S209.

In the step S207, the focus controller 203 (estimator 110) calculatesthe shift frequency ΔFREQ from the setting oscillatory frequency FREQ soas to shift both the first and second estimated modulated frequencies tothe outside of the prohibited frequency band, and provides the frequencyshift process for calculating the post-shift setting oscillatoryfrequency FREQ′. The second estimate modulated frequency has a nonlinearcharacteristic for a frequency change unlike the first estimatedmodulated frequency. Since the first estimated modulated frequency>thesecond estimated modulated frequency, the shift frequency ΔFREQ iscalculated in accordance with the following sequence in consideration ofa value range of the prohibited frequency band set in this embodiment.

FIG. 9 illustrates changes of the first and second estimated modulatedfrequencies as the setting oscillatory frequency changes in thisembodiment. The abscissa axis denotes a setting oscillatory frequency,the ordinate axis denotes a modulated frequency. A  plot connected by asolid line is the first estimated modulated frequency (“estimatedfrequency 1” in FIG. 9), and a  plot connected by a solid line is thesecond estimated modulated frequency (“estimated frequency 2” in FIG.9). In FIG. 9, masked belt areas A and B are prohibited frequency bandsto the first and second estimated modulated frequencies and the area Cis an area in which the first and second estimated modulated frequenciescan be located. The shift frequency ΔFREQ is calculated so that thefirst and second estimated modulated frequencies or the first and secondmodulated frequencies can be located in the area C.

The estimator 110 calculates the shift frequency ΔFREQ as follows.Initially, the estimator 110 determines which of the first and secondestimated modulated frequencies is located in the prohibited frequencyband. When the first estimated modulated frequency is located in theprohibited frequency band, the process differs according to the value ofthe first estimated modulated frequency.

When the first estimated modulated frequency FREQ_(est.1)<10 kHz, theestimator 110 shifts the first modulated frequency so that the firstmodulated frequency is located on the low frequency side of theprohibited frequency band as in the following expression:

ΔFREQ=(FREQ_(est.1)−2 kHz)/Q ₁

Herein, Q₁ is the number of additions up to the overflow in the firstcount period, and 2 kHz is the lowest frequency in the prohibitedfrequency band for the first estimated modulated frequency. A sign ofΔFREQ becomes minus when S₁−S₂ becomes a negative value, meaning a shiftto the low frequency side. The sign of ΔFREQ becomes plus when S₁−S₂becomes a positive value, meaning a shift to the high frequency side.The first estimated modulated frequency is below 2 kHz for thepost-shift setting oscillatory frequency FREQ′, and the second estimatedmodulated frequency is lower than the first estimated modulatedfrequency or lower than 2 kHz. Thus, neither the first nor secondestimated modulated frequency is located in the prohibited frequencyband.

On the other hand, when the first estimated modulated frequencyFREQ_(est.1)≧10 kHz, the estimator 110 shifts the first estimatedmodulated frequency so that the first modulated frequency is located onthe high frequency side of the prohibited frequency band as in thefollowing expression:

ΔFREQ=(12 kHz−FREQ_(est.1))/Q ₁

12 kHz is the highest frequency (FRWQ_(spc)) in the prohibited frequencyband for the first estimated modulated frequency. A sign of ΔFREQbecomes plus when S₁−S₂ becomes a negative value, meaning a shift to thehigh frequency side. The sign of ΔFREQ becomes minus when S₁−S₂ becomesa positive value, meaning a shift to the low frequency side.

The estimator 110 determines whether the second estimated modulatedfrequency FREQ_(est.2) is located outside of the prohibited frequencyband with the post-shift setting oscillatory frequency FREQ′. Unless thesecond estimated modulated frequency FREQ_(est.2) is located outside ofthe prohibited is frequency band, the setting oscillatory frequency isagain shifted in the same direction as that of ΔFREQ. By repeating thisprocess a plurality of times, the setting oscillatory frequency FREQ′can be searched in which both the first and second estimated modulatedfrequencies are located outside of the prohibited frequency band.

When the second estimated modulated frequency is not located outside ofthe prohibited frequency band, the estimator 110 performs a processequivalent with that for the case where the first estimated modulationfrequency FREQ_(est.1)≧10 kHz. A shift direction of the settingoscillatory frequency may be a direction in which the current firstestimated modulated frequency separates from the prohibited frequencyband (12 kHz).

Thus, the post-shift setting oscillatory frequency FREQ′ can becalculated in which both the first and second estimated modulatedfrequencies are located outside of the prohibited frequency band.

Next, in the step S208, the focus controller 203 (estimator 110)calculates the added value CNT_(add) for each clock for the adder 101corresponding to the post-shift setting oscillatory frequency FREQ′calculated in the step S207. Similar to the step S204, the added valueCNT_(add) is calculated as follows where CNT_(max) is the count upperlimit value and CLK is the clock:

CNT_(add)=FREQ′×(CNT_(max)+1)/CLK

Thereafter, the focus controller 203 moves to the step S209.

In the step S209, the focus controller 203 (CPU 120) settles thepost-shift setting oscillatory frequency FREQ′ calculated by theestimator 110 as information output to the oscillator 100. When it isdetermined that the modulated frequency that occurs with the settingoscillatory frequency FREQ in the step S206 is not located in theprohibited frequency band, a relationship of FREQ=FREQ′ is established.The setting oscillatory frequency settled in this process becomes astart frequency, and the oscillatory frequency in the phase differencecontrol over the vibration motor.

Next, in the step S210, the focus controller 203 (CPU 120) outputs anoutput enablement ENABLE to the oscillator 100. Moreover, the CPU 120outputs the set duty ratio DUTY set in the step S203, the set phasedifference PHASE between the A and B modes, and the post-shift settingoscillatory frequency FREQ′ settled in the step S209, to the oscillator100. This process electrifies the vibration motor, and actually startsdriving the focus lens 202.

Next, in the step S211, the focus controller 203 (CPU 120) calculates aposition deviation between the current position of the focus lens 202obtained from the focus position detector 150 and the target positionset in the step S201.

Next, in the step S212, the focus controller 203 (CPU 120) determineswhether the position deviation calculated in the step S211 becomes 0 orthe focus lens 202 has reached the target position. The CPU 120 moves tothe step S213 when the focus lens 202 has reached the target position,and moves to the step S215 when the focus lens 202 has not yet reach thetarget position.

In the step S213, the focus controller 203 (CPU 120) maintains theelectrification for a predetermined time period after the focus lens 202reaches the target position. The focus controller 203 sets the phasedifference between the A and B modes to 0 while maintaining theelectrification, and generates the standing wave in the oscillatingobject. This electrification maintenance restrains the focus lens 202from passing the target position due to the inertia and from stoppingthere.

This embodiment determines that the focus lens 202 reaches the targetposition by determining that the target position is equal to the currentposition (or the position deviation is 0). However, it may be determinedthat the focus lens 202 reaches the target position when the currentposition of the focus lens 202 falls in a range |target position±x|, andthe subsequent electrification maintenance may be a position feedbackcontrol so as to zero the fine deviation.

Next, in the step S214, the focus controller 203 (CPU 120) stopsmaintaining the electrification at the target position, and completesprocess for the camera side or lens side focus driving command obtainedin the step S201. A series of processes ends for driving of the focuslens 202.

In or after the step S215, the focus controller 203 (CPU 120) determinesthe driving state of the vibration motor (acceleration or decelerationdriving or constant speed driving), and controls driving of thevibration motor.

In the step S215, the focus controller 203 (CPU 120) compares a positiondeviation between the current position of the focus lens 202 and thetarget position, with a deceleration driving amount up to the stopobtained from the deceleration profile with the current speed. The focuscontroller 203 determines, based on the comparison result, whether thefocus lens 202 has reached the deceleration start position. When theposition deviation is equal to or smaller than the deceleration drivingamount, the CPU 120 determines that the focus lens 202 has reached thedeceleration start position, and moves to the step S216. When the focuslens 202 does not reach the deceleration start position, the flow movesto the step S219.

In the step S216, the focus controller 203 (CPU 120) determines whetherthe current setting oscillatory frequency is raised up to the startfrequency. In this step, the vibration motor is in the decelerationstate. In the deceleration state, this embodiment decelerates thevibration motor with a deceleration according to the decelerationprofile. The CPU 120 raises the setting oscillatory frequency up to thestart frequency in accordance with the deceleration profile when thefrequency control is performed just before the vibration motor isdecelerated, and performs the phase difference control so as to promotethe deceleration process when the setting oscillatory frequency reachesthe start frequency. On the other hand, when the phase differencecontrol is performed just before the deceleration, the CPU 120 performsthe deceleration process with the phase difference control.

In this step, the CPU 120 confirms whether the setting oscillatoryfrequency has the same value as the start frequency in the decelerationprocess, and determines which of the frequency control or the phasedifference control is used for the next control. When the settingoscillatory frequency is equal to or higher than the start frequency,the CPU 120 moves to the step S218. When the setting oscillatoryfrequency is lower than the start frequency, the CPU 120 moves to thestep S217.

This embodiment does not set the setting oscillatory frequency to avalue higher than the start frequency in the frequency control in thedeceleration. In switching to the phase difference control, the settingoscillatory frequency is set to the same value as the start frequency.Thereby, it is guaranteed that the oscillatory frequency that avoids themodulated frequency is set in the phase difference control in thedeceleration.

In the step S217, the focus controller 203 (CPU 120) fixes the phasedifference between the A and B modes based on the deceleration profile,and changes the setting oscillatory frequency to the high frequencyside. The CPU 120 that has performed this process returns to the stepS210 and provides a frequency control.

On the other hand, in the step S218, the focus controller 203 (CPU 120)sets (fixes) the oscillatory frequency to the same value as the startfrequency based on the deceleration profile, and reduces the phasedifference between the A and B modes. The CPU 120 that has performedthis process returns to the step S210 and performs a phase differencecontrol.

In the step S219, the focus controller 203 (CPU 120) determines whetherthe driving state of the vibration motor is in an accelerated state orin a fixed speed state. The acceleration state can be determined whenthe CPU 120 currently refers to the acceleration profile or when a speeddeviation between the current speed and a higher commanded speed(driving speed contained in the driving command) is equal to or higherthan the predetermined value. When the driving state is not theacceleration state, the fixed speed state can be determined. The CPU 120moves to the step S220 in the acceleration state, and moves to the stepS223 in the steady state.

In the step S220, the focus controller 203 (CPU 120) determines thecurrent phase difference between the A and B modes. When the phasedifference is below 90 degrees, the CPU 120 moves to the step S222 forthe phase difference control, and when the phase difference is equal toor above 90 degrees, the CPU 120 moves to the step S221 for thefrequency control.

In the step S221, the focus controller 203 (CPU 120) fixes the phasedifference between the A and B modes based on the acceleration profile,and changes the setting oscillatory frequency to the low frequency side.The CPU 120 that has performed this process returns to the step S210 forthe phase difference control.

In the step S222, the focus controller 203 (CPU 120) sets (fixes) theoscillatory frequency to the same value as the start frequency based onthe acceleration profile, and increases the phase difference between theA and B. The CPU 120 that has performed this process returns to the stepS210 for the phase difference control.

In the step S223, the focus controller 203 (CPU 120) determines acurrent speed deviation. After this step, the process for the fixedspeed state is performed but the speed feedback control is performed soas to restrain fine speed fluctuations caused by the load fluctuations.The CPU 120 moves to the step S224 for a fine acceleration process whenthe current speed is lower than the commanded speed, and moves to thestep S225 for a fine deceleration process when the current speed ishigher than the commanded speed.

In the step S224, the focus controller 203 (CPU 120) determines thecurrent phase difference between the A and B modes. When the phasedifference is equal to or above 90 degrees, the CPU 120 moves to thestep S226 for the phase difference control by fixing the phasedifference, and when the phase difference is below 90 degrees, the CPU120 moves to the step S227 for the phase difference control.

In the step S226, the focus controller 203 (CPU 120) fixes the phasedifference since the phase difference reaches 90 degrees in the justprevious control, and changes the oscillatory frequency. For the fineacceleration process, the CPU 120 sets the oscillatory frequency lowerthan the current oscillatory frequency and drives the vibration motor.The CPU 120 that has performed this process returns to the step S210.

In the step S227, the focus controller 203 (CPU 120) further increasesthe phase difference and torque of the vibration motor since the phasedifference has not yet reached 90 degrees. The CPU 120 that hasperformed this process returns to the step S210.

In the step S225, the focus controller 203 (CPU 120) estimates thecurrent oscillatory frequency. The CPU 120 moves to the step S228 forthe phase difference control when the oscillatory frequency is equal toor below the start frequency, and moves to the step S229 for thefrequency control when the oscillatory frequency is higher than thestart frequency.

In the step S228, the focus controller 203 (CPU 120) reduces the phasedifference and restrains the torque of the vibration motor for thedeceleration process. The CPU 120 that has performed this processreturns to the step S210.

In the step S229, the focus controller 203 (CPU 120) makes higher theoscillatory frequency and restrains the torque for the vibration motorfor the deceleration process. The CPU 120 that has performed thisprocess returns to the step S210.

As described above, this embodiment estimates the first and secondmodulated frequencies that occur in the PDM control, and shifts the setfrequency in accordance with the estimation result. This configurationdrives the vibration motor and moves the focus lens 202 without causingthe first and second modulated frequencies to be located in theprohibited frequency band.

According to this embodiment, the interchangeable lens 200 estimates thefirst and second modulated frequencies that occur in the oscillator 100,and shifts the setting oscillatory frequency so that the estimationresult can provide that they are located outside of the prohibitedfrequency band. However the time information may be provided to theinformation of the estimation result and output to the camera 300, andthe camera 300 may remove or reduce, based on the information, thefrequency band of the modulated frequency as noises relating to thefirst and second modulated frequencies from the recorded audioinformation.

While this embodiment discusses the lens interchangeable type camerasystem, the frequency shift process described in this embodiment can beperformed in driving the vibration motor configured to drive the opticalelement, such as a lens, in the lens integrated type camera (opticalapparatus).

Each of the embodiments can provide a frequency control apparatusconfigured to estimate an undesired mixed frequency that occurs in thefrequency control in the PDM system, and to prevent the mixed frequencyfrom being contained in the specific band. When the frequency controlapparatus is installed in the motor driving apparatus or image capturingapparatus, a problem, such as a noise and an uneven speed, can berestrained.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2015-240719, filed on Dec. 10, 2015 which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A frequency control apparatus comprising: a signal generator configured to generate an output signal as a digital signal having a target frequency that has been set, using a plurality of signals having frequencies that are different from the target frequency and one another; an estimator configured to estimate a mixed frequency that is a frequency of a signal component mixed in the output signal and different from the target frequency and each of frequencies of the plurality of signals; and a frequency shift unit configured to shift at least one of the target frequency and the frequencies of the plurality of signals in accordance with an estimation result of the mixed frequency.
 2. The frequency control apparatus according to claim 1, wherein the frequency shift unit shifts at least one of the target frequency and the frequencies of the plurality of signals, when the mixed frequency that has been estimated is included in a specific frequency band.
 3. The frequency control apparatus according to claim 2, wherein the specific frequency band is an audible band of a human, and a frequency band lower than the target frequency.
 4. The frequency control apparatus according to claim 1, wherein the signal generator generates the output signal by an adder system including: a counter configured to increase a count value by each added value at a predetermined period from a count lower limit value to a count upper limit value; and a comparator configured to switch high and low states of the output signal in accordance with whether the count value is larger or smaller than a predetermined value between the lower limit value and the count upper limit value.
 5. The frequency control apparatus according to claim 4, wherein the estimator estimates a low range frequency lower than at least one of a plurality of mixed frequencies using a calculation using the count upper limit value and the added value.
 6. The frequency control apparatus according to claim 2, wherein the estimator estimates a low range frequency lower than at least one of the plurality of mixed frequencies, and wherein the frequency shift unit shifts the frequency of at least one of the plurality of signals when the low range frequency is contained in the specific frequency band, and calculates a shift amount of the frequency of at least one of the plurality of signals using the low range frequency and a maximum frequency of the specific frequency band.
 7. A motor driving apparatus configured to drive a vibration motor by applying a frequency signal to an electrical-mechanical energy conversion element, by exciting a vibration in the vibrator, and by relatively moving the vibrator and a contact member that contacts the vibrator, the motor driving apparatus comprising: a signal generator configured to generate an output signal as a digital signal having a target frequency that has been set, using a plurality of signals having frequencies that are different from the target frequency and one another; an estimator configured to estimate a mixed frequency that is a frequency of a signal component mixed in the output signal and different from the target frequency and each of frequencies of the plurality of signals; and a frequency shift unit configured to shift at least one of the target frequency and the frequencies of the plurality of signals in accordance with an estimation result of the mixed frequency.
 8. A motor driving apparatus according to claim 7, wherein the motor driving apparatus generates a plurality of frequency signals having phases that are different from one another, wherein the motor driving apparatus drives the vibration motor by switching a phase difference control that maintains constant frequencies of the plurality of frequency signals and changes a phase difference, and a frequency control that maintains constant a phase difference of the plurality of the plurality of frequency signals and changes the frequency, and wherein the shift unit shifts the target frequency in the phase difference control.
 9. The motor driving apparatus according to claim 7, wherein the frequency shift unit shifts the target frequency when the target frequency is contained in the specific frequency band, and the specific frequency band contains a resonance frequency of the vibration motor.
 10. An optical apparatus comprising: a vibration motor; and a motor driving apparatus configured to drive the vibration motor by applying a frequency signal to an electrical-mechanical energy conversion element, by exciting a vibration in the vibrator, and by relatively moving the vibrator and a contact member that contacts the vibrator, wherein the motor driving apparatus includes: a signal generator configured to generate an output signal as a digital signal having a target frequency that has been set, using a plurality of signals having frequencies that are different from the target frequency and one another; an estimator configured to estimate a mixed frequency that is a frequency of a signal component mixed in the output signal and different from the target frequency and each of frequencies of the plurality of signals; a frequency shift unit configured to shift at least one of the target frequency and the frequencies of the plurality of signals in accordance with an estimation result of the mixed frequency; and an optical element driven by the vibration motor.
 11. A non-transitory computer-readable storage medium configured to store a program for controlling a frequency control apparatus configured to generate an output signal as a digital signal having a target frequency that has been set, using a plurality of signals having frequencies that are different from the target frequency and one another, the program enabling a computer to execute a method including the steps of: estimating a mixed frequency that is a frequency of a signal component mixed in the output signal and different from the target frequency and each of frequencies of the plurality of signals; and shifting at least one of the target frequency and the frequencies of the plurality of signals in accordance with an estimation result of the mixed frequency. 